Der Obstsalat mit Mandarine schmeckt auch am nächsten Morgen gut.

Because Obstsalat is a masculine noun.

A useful rule for German compound nouns is that the last part determines the gender. Here, the last part is Salat, and that noun is masculine: der Salat.

So:

• der Salat
• der Obstsalat

Schmecken means to taste.

So Der Obstsalat ... schmeckt gut literally means The fruit salad tastes good.

German often uses schmecken where English might sometimes say:

• tastes good
• is tasty
• still tastes fine

It is more specific than ist gut, because schmecken is about taste, not just general quality.

This is a very natural question, because several versions are possible depending on what exactly you want to say.

First, mit always takes the dative case.

So grammatically:

• mit einer Mandarine = with a mandarin
• mit Mandarinen = with mandarins
• mit der Mandarine = with the mandarin

In your sentence, mit Mandarine has no article. That can sound a bit like an ingredient label or recipe style: fruit salad with mandarin.

A learner should know that:

• mit einer Mandarine emphasizes one mandarin
• mit Mandarinen sounds more like mandarins as an ingredient in general
• mit Mandarine is understandable, but in everyday speech many speakers might more naturally say mit Mandarinen or mit einer Mandarine, depending on the meaning

Also, even though mit requires dative, the noun Mandarine does not visibly change here when no article is used.

Because in German, the case is not always visible on the noun itself.

With many feminine singular nouns, the noun form often stays the same, especially when there is no article.

Compare:

• die Mandarine — nominative
• mit der Mandarine — dative

The dative is clearly visible in der.

But in:

• mit Mandarine

the noun Mandarine itself does not show a special dative ending. The case is understood because mit requires dative.

Am is a contraction of an dem.

So:

• am nächsten Morgen = an dem nächsten Morgen

In time expressions, am is very common:

• am Montag = on Monday
• am Abend = in the evening
• am nächsten Morgen = the next morning / on the next morning

Because am = an dem, and dem is dative masculine/neuter singular here.

Morgen is a masculine noun in this expression:

• der Morgen

So after dem, the adjective takes the ending -en:

• dem nächsten Morgen

That is why the full phrase is:

• am nächsten Morgen

Because it is a noun here, and German nouns are capitalized.

In this sentence:

• Morgen = morning (noun)

Compare that with:

• morgen = tomorrow (adverb)

So:

• am nächsten Morgen = the next morning
• morgen = tomorrow

That capitalization difference is very important in German.

Auch usually means also, too, or as well.

In this sentence, it means that the fruit salad tastes good not only earlier, but also the next morning.

Depending on context, natural English translations might be:

• The fruit salad with mandarin also tastes good the next morning.
• The fruit salad with mandarin still tastes good the next morning.
• The fruit salad with mandarin tastes good even the next morning.

So auch adds the idea of in addition / still / even then.

Because German main clauses normally follow the verb-second rule.

Here the structure is:

• Der Obstsalat = element 1
• schmeckt = finite verb in position 2
• auch am nächsten Morgen gut = the rest of the sentence

So once Der Obstsalat is placed first, schmeckt must come next.

After that, German has some flexibility with adverbs and phrases, but this version sounds very natural:

• Der Obstsalat mit Mandarine schmeckt auch am nächsten Morgen gut.

Because gut is describing how the fruit salad tastes, and in German that kind of information often comes late in the clause.

A simple version is:

• Der Obstsalat schmeckt gut.

If you insert extra information such as auch am nächsten Morgen, that extra information goes before gut:

• Der Obstsalat schmeckt auch am nächsten Morgen gut.

So the sentence ends with the final evaluation: gut.

Yes. Even if still is not written explicitly in German, English often uses it to make the sentence sound natural.

So a very natural translation is:

• The fruit salad with mandarin still tastes good the next morning.

That still comes from the overall meaning created by:

• auch
• am nächsten Morgen

Together, they suggest that the fruit salad remains good later than you might expect.

It is a very common expression, yes.

It means:

• the next morning
• on the following morning

Similar expressions are:

• am nächsten Tag = the next day
• am nächsten Abend = the next evening
• in der nächsten Woche = next week

So this is a useful pattern to learn:

• am + adjective + time noun